I then type % testwatch or % testwatch TEST_VERBOSE=1 in the root directory of any module I'm messing with.
This won't work 100% of the time but hits that 80/20 spot for me.

I have a little todo list on an improved test monitor that I will, when some of that mythical free time comes along, implement. Now we have the lovely Test::Harness::Straps it's not even that difficult.